00:01
Hey there, welcome to numerate.
00:03
We are asked to find the expecting number of children of a family, knowing that they will stop there if the first child is a boy.
00:13
So if a first child is a boy, they will stop.
00:16
If it's a girl and then a boy, then they will stop.
00:19
If it's a girl, another girl, another girl, and then a boy, they will stop.
00:25
So there's basically a lot of outcomes that are possible.
00:30
So for part a, we're going to find the expected number of children, knowing that this here follows a geometric distribution.
00:41
Knowing this, we know that p is basically for a boy or a girl is going to equal exactly one half.
00:51
Knowing this right here, we can find our expected value here.
01:00
So the expected value of a family will basically equal.
01:12
We have x given the first child is a girl.
01:19
So first is a girl.
01:23
Equaling 1 divided by 1 minus 1 half, which equals 1 half, which equals 2.
01:36
So what we can do here to find our overall expected value, though, is to take our probability 1 half and multiply by 1 plus 1 plus 1 plus 1 half times our expected value we found above equals 2...